1. Field of the Invention
The present invention relates to the field of liquid crystal display (LCD), and in particular to a common circuit for gate driver on array (GOA) test and eliminating power-off residual images.
2. The Related Arts
As the liquid crystal display (LCD) shows the advantages of being thin, low power-consumption, and no radiation, the LCD is widely used in various devices, such as, liquid crystal TV, mobile phones, PDA, digital camera, PC monitors or notebook PC screens as well as tablet PCs.
The available LCDs are mostly backlight type, which includes an LCD panel and a backlight module. The operation theory behind the LCD panel is to inject liquid crystal molecules between the thin film transistor (TFT) array substrate and the color filter (CF), and then apply a driving voltage to control the rotation direction of the liquid crystal molecules to refract the light from the backlight module to generate the image.
The display area of LCD panel includes a plurality of pixels arranged in matrix, with each column of pixels electrically connected to a scan line and each row of pixel electrically connected to a data line. As shown in FIG. 1, m and n are both positive integers. The pixel driver circuit of the pixel at the n-th column and m-th row includes a thin film transistor T. The gate of T is connected to the horizontal gate scan line Gate(n) of the n-th column. The drain of T is connected to the vertical data line Data(m) of the m-row. The source is connected to the corresponding pixel electrode. The equivalence of a liquid crystal capacitor Clc and a storage capacitor Cst connected in parallel exists between the source of T and the common voltage line Com. When the LCD panel functions normally, a sufficient positive voltage applied to the scan line will make all the Ts on the gate scan line conductive to load data signal from the data line into the pixel electrode to control the transmittance of different liquid crystal molecules to achieve the color control effect to display an image. The liquid crystal capacitor Clc and the storage capacitor Cst of the LCD panel will accumulate electric charges during normal operation. When powered off, the accumulated electric charges do not receive proper release, resulting in DC residual in the liquid crystal molecules to cause residual images on the LCD panel, often referred to as power-off residual images.
The driving of the gate scan line of LCD panel is first accomplished by the external integrated circuit (IC). The external IC is able to control the stepwise charge and discharge of the gate scan line. The gate driver on array (GOA) technology uses the array manufacturing process of LCD panel to form driver circuit of the gate scan line in the surrounding area of the display area of the substrate to replace the external IC to perform the gate scan line driving. GOA technology can reduce the bonding process for external IC to improve yield rate and reduce manufacturing cost. Moreover, the GOA technology also makes LCD panel easier for narrow border or borderless display product.
Because the TFT electrical stability and uniformity affects the GOA circuit yield rate, GOA circuit must be tested. A common test is to test the output signal of the final stage GOA unit to determine whether the GOA circuit is normal. However, this type of test can only test the output signal of the final GOA unit, and is unable to determine specifically which stage of GOA unit is faulty, which limits the analysis and improvement on the GOA circuit.